Photometric measurements of Echo I satellite on specular degradation of aluminized Mylar surface during orbi

Emmons, R. H.

English

NASA Technical Reports Server

t I b 
GOODYEAR AEROSPACE 
CORPORATION 
AN lNDICATED SPECULAR DEGRADATION 
RATE FOR ALUMINIZED MYLAR SVRFACES IN 
NEAR-EARTH ORBIT FROM RECENT PHOTOMETRIC 
OBSERVATIONS O F  THE ECHO I SATELLITE 
by 
Richard H. Lmmons 
Goodyear Aerospace Corporation 
(A paper presented before the 116th meeting of the 
American Astronomica.1 Society in Flagstaff, Ar iz .  
24-27 June 1964.) 
GER-11521, Rev A 17 June 1964 
- 7 -  
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ABSTRACT OF 
A N  INDICATED SPECULAR DEGRADATION 
RATE FOR ALUMINIZED MYLAR SURFACES I N  
NEAR-EARTH ORBIT FROM RECENT PHOTOMETRIC 
OBSERVATIONS O F  THE ECHO I SATELLITE 
by 
Richard H. Emmons 
Goodyear Aerospace Corporation 
Photometric measurements  were made of the Echo I satell i te with a visual 
comparison photometer on 1 March 1964 (Universal  T ime) .  
The data, taken over a wide range of phase angles (143 to 32 deg) and nor-  
mal ized for  slant range, a r e  best fitted in illuminance versus  Russel l ' s  phase 
function by a surface model that is 96 percent specular and 4 percent diffuse. 
This  indicates that the actual specular degradation r a t e  for aluminized Mylar 
sur faces  in a near-ear th  orbit ,  due to the combined effects of a l l  environ- 
mental  fac tors ,  is l e s s  than 1 percent per year .  
If a reflectivity coefficient of 0 . 8 3  is assumed,  the Echo I photometric obser -  
vations yield a mean radius of curvature of 47 ft with a probable e r r o r  of 3 ft .  
Several  surface anomalies were observed having local rad i i  of curvature rang-  
ing f rom 39 to 66 ft .  
Together with the resu l t s  f rom laboratory hypervelocity impact tes t s  of very 
small par t ic les  on aluminized Mylar, the present  indications may prove of 
value in further defining the micrometeoroid environment at Echo 1 ' s  orbital 
height, either with respect  to the flux in the vicinity of the m a s s  cutoff or  the 
mass cutoff i tself .  
dicting the useful life in nearby space of exposed optical and thermal  balance 
sur faces .  
The present indications should a l so  prove of value in p re -  
The photometric studies of Echo I a r e  being extended at Goodyear Aerospace 
Corporation under NASA-Langley Resear'ch Center Contract NAS 1-31 14, 
monitored by William J .  O'Sullivan. While final resu l t s  f rom these additional 
visual and photoelectric measurements  a r e  not available a t  this t ime, the p re -  
l iminary resu l t s  appear to support the conclusion here in  that Echo 1's surface 
r ema ins  highly specular.  
8 
ABSTRACT 
Photometric measurements  were made of the Echo I satell i te with a visual 
comparison photometer on 1 March 1964 (Universal  Time).  
The data, taken over a wide range of phase angles (143 to 32 deg) and nor-  
malized for  slant range, a r e  best fitted in illuminance ve r sus  Russe l l ' s  phase 
function by a surface model that  is 96 percent specular and 4 percent diffuse. 
This indicates that the actual specular degradation r a t e  for aluminized Mylar 
su r faces  in a near -ear th  orbit ,  due to the combined effects of all environ- 
mental  fac tors ,  is l e s s  than 1 percent per yea r .  
If a reflectivity coefficient of 0 .  83 is assrzmed, the Echo I photometric obser -  
vations yield a mean radius of curvature of 47 ft  with a probable e r r o r  of 3 ft .  
Several  surface anomalies were  observed having local radi i  of curvature rang-  
ing f rom 39 to 66 f t .  
Together with the resu l t s  f rom laboratory hypervelocity impact tes t s  of very 
small par t ic les  on aluminized Mylar, the present  indications may prove of 
value in further defining the micrometeoroid environment a t  Echo 1 ' s  orbital  
height, either with respect  to the flux in the vicinity of the mass cutoff or the 
mass cutoff itself. The present indications should also prove of value in p re -  
dicting the useful life in nearby space of exposed optical and thermal  balance 
su r  fac e s . 
The photometric studies of Echo I a r e  being extended a t  Goodyear Aerospace 
Corporation under NASA-Langley Research  Center Contract NAS 1-31 14, 
monitored by William J .  O'Sullivan. While final resu l t s  f rom these additional 
visual  and photoelectric measurements  a r e  not available a t  this t ime, the p re -  
l iminary resu l t s  appear to support the conclusion herein that Echo 1 ' s  surface 
remains  highly spe'cular . 
. GER-11521A 
T A B L E O F C O N T E N T S  
Page Section Title . 
. . . . . . . . . . . . . . . . .  1 I INTRODUCTION 
. . . . . . .  I1 SURFACE MICROTEXTURE ANALYSIS 7 
. . . . . .  9 
10 
111 SURFACEMACROTEXTUREANALYSIS 
IV SIGNIFICANCE OF RESULTS . . . . . . . . . . .  
. . . . . . . . . . . . . . . . . . .  LIST OF R E F E R E N C E S .  12 
... 
-111- 
. 
Goodyear Aerospace GER-11521A 
SECTION I - INTRODUCTION 
To obtain photometric data for bright ar t i f ic ia l  satell i tes,  a hand-held, polar - 
izing, visual-comparison photometer was designed and constructed a t  Good- 
year  Aerospace Corporation in January, 1964a ( s e e  Figure 1) .  
readouts (polarizing f i l ter  rotations) are converted to s te l lar  magnitudes by 
means  of the calibration determined f rom repeated observations of s t a r s  of 
known visual magnitude. l Y  
according to the instantaneous zenith distances (z) of the reference stars and 
The digital 
Allowances a r e  made for atmospheric extinction 
target .  
With this instrument 21 photometric measurements  were  made of Echo I f rom 
North Canton, Ohio, (Smithsonian Astrophysical Observatory satell i te t rack-  
ing station No. 8544) in a 13.6-min period, during a high pass  of this satell i te 
on 1 March 1964 Universal Time (U. T. ) .  
minute exposure photograph taken a t  0 h r  3 7  min U. T . ,  1 March 1964, show- 
ing Echo 1's path left of the planets Venus and Jupiter as the f i r s t  photometric 
observations were  made. Also shown a r e  selected star and constellation lo- 
cations, r ight ascension/declination reference grid,  and t ime t ics .  
Figure 2 was drawn f rom a one- 
Calibration observations of s t a r s  were  made before and af ter  the satell i te date 
was taken, yielding a total of 39 measurements  a t  18 different elevations of 17 
different re ference  magnitudes throughout the photometer 's  range. 
squares  reduction was made of this data, providing a mean extinction coeffi- 
cient of 0 .  207 and the instrument 's  calibration equation: 
A least  
a This photometer was first t r ied in its automatic r eco rd  mode to measu re  
Echo 11's optical character is t ics  during its f i r s t  week in orbi t .  
u rements  obtained were consistent with predicted values that would resu l t  
f rom a successful deployment of this satellite. 
The m e a s -  
bSuperior numbers in the text re fer  to i tems  in the Lis t  of References.  
b - 1  - 
Goodyear  A e r o s p a c e  GER-  1 1  521A 
2-IN. OUTSIDE DIAMETER . PROVISION FOR 
ALUM? TARGET FILTER 
I 
WINDOW T I L T  ADJUSTMENT 
THIN GLASS WINDOW 
E Y E  CUP 
. TARGET FILTERS 
qODIAL, ADAPTER 
L T E R  BATTERYHOLDER 
N.D. = 0.50 N.D. = 0.70 N.D. = 2.00 
A m  = t1.25 Am = t1 .75  Am = t5 .00  
NOTE: 
N.D. = NEUTRAL DENSITY 
3-V GRAIN OF WHEAT B U L B  - POTENTIOMETER FOR ELECTRIC 
READOUT FOR OPTIONAL AUTO- 
MATIC RECORDING MODE 
5- BY 5-IN. ROTATING 
POLARIZING FILM 
F i g u r e  1 - Visual  Compar i son  P h o t o m e t e r  f o r  B r i g h t  Sa te l l i t e s  
- 2 -  
Goodyear Aerospace GER-11521A 
F 
0 
Figure  2 - Echo 1's Apparent Path Past Jupiter and Venus 
- 3  - 
Goodyear Aerospace GER-11521A 
m t 0. 207X = 6. 446 - 3. 802 log (instrument reading) , 0 
where 
m = the extra atmosphere magnitude, and 
0 
a X = number of a tmospheres  (g sec  z ) .  
The standard deviation of the calibration data was 0 .  196 s te l lar  magnitude, 
which includes the effect  of possible extinction changes. 
efficient was 0.  9836. 
The correlation co- 
Table I gives the Universal Times (obtained via short-wave radio f rom CHU 
and tape recorded together with the photometer readings),  the instrument 
readings,  the phase angle, t h e  reduced s te l lar  magnitudes normalized to a 
1000-stat-mi zenith range, and the indicated radius  of curvature .  
magnitudes have been cor rec ted  for earthshine.2y3 At the tracking station where 
these  data were  taken, the longitude was 81 deg 24 min 42 sec  west, the lati-  
tude was 40 deg 52 min 45 sec north, and the elevation was 350 m above sea  
level.  
The stellar 
The phase angles and geometrical c i rcumstances of these observations were  
reduced f rom orbital  elements provided by the Smithsonian Astrophysical Ob- 
servatory,  which were  found to conform to observed times and positions obtained 
during the pass. 
22 h r ,  48 min; declination, -7 deg 39 min. 
The solar coordinates a t  this t ime were: right ascension, 
The normalized s te l lar  magnitudes given in Table I a r e  plotted versus  phase 
angle in F igure  3. Upon inspection of the data i t  was judged that the three  un- 
numbered photometric values were the resu l t  of surface macrotexture  anoma- 
l ies ,  and they were  therefore excluded f rom the microtexture analysis.  
remaining 18 numbered data points, used in the subsequent microtexture analy- 
sis, yield a mean normalized stellar magnitude of to. 22. 
The 
2 - Actually used X = sec z - 0. 0018167(sec z - 1) - 0. 002875(sec z - 1) 
0.0008083(sec z - 1) 
a 
3 ( see  Reference 4).  
Goodyear Aerospace GER-11521A 
it * I +  
0 9 N ~ o t - c a d ~ * 6 t - N m O m - o m m ~  
m O m t - N * ~ N * * * m * m * O d 9 0 ~ *  
N ~ O - m N m m N m m * N m O ~ N O m O O  
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0  
I I 1  I 
u v v  
a ) Q ) Q )  
m m m  
9 N . 0  
m o *  
.!i .B .5 
E E E  
2 2 2  
t - 6 6  
0 r . l m  
0 0 0  
m * m  6 0  - t - Q ) .  
v u v  
a l a e ,  
m m m  
2 2 2  
0 0 0  
. .  
- . .  
M 
v v v  
Q ) o c  
m m m  
m o m  
N O 0  
0 
ca 
0 
0 
x 
> 
V 
e, 
w 
al 
k 
w 
0 
c, 
E: 
e, 
V 
w 
0) 
0 
V 
Id 
w 
U .r( 
.d U 
4 
.r( 
.d 
m 
m $
m 
c 
-5 -  
. Goodyear Aerospace GER-11521A 
9 - 
I 
0 
IL 
I- 
V w 
0 i 
0 9 
N 
8 
c 
8 
c 
:: 
c 
8 
c 
8 
8 
3 0
- 
v) 
W 
W 
U u 
W 
W 
-I 
0 
z 
U 
W 
m 
I 
3 0  
N 
a 
a 
Figure  3 - Echo I normalized Magnitudes ve r sus  Phase  -4ngle 
-6 - 
Goodyear Aerospace GER-11521A 
SECTION I1 - SURFACE MICROTEXTURE ANALYSIS 
A regress ion  analysis was performed on the 18 normalized magnitudes (m) 
with a IBM 1410 computer. 
5 nances (E) on the Russell  
fusely reflecting sphere that obeys Lamber t ' s  law. 
on the following regress ion  equation: 
The dependence of their corresponding illumi- 
phase function F($) , was investigated for a dif- I 1  
This analysis was based 
- E = antilog(-0. 4 m) 
EO 
where  
E / E ~  = illuminance ratio, 
A = weighting factor for optically specular reflection, 
B = weighting factor for optically diffuse reflection, 
F($) = 1 [s in  t,!J t (n -t,!J) cos$]  , and n 
9 = phase angle (0  deg when satell i te is opposite sun). 
A least squares  best-fit solution of this regress ion  equation for the normalized 
data yields: 
A = 3. 13621, 
B = 0. 14424, 
correlat ion coefficient = 0. 27, 
and 
standard deviation, (I = *O. 15 . 
. 
Goodyear Aerospace GER- 1 152 1A 
This solution, t ransformed to stellar magnitudes, is plotted in Figure 3 ,  to- 
gether with curves for  best-fi t  solutions where A = 0 (surface 100 percent 
diffuse), and B = 0 (surface 100 percent specular).  
The present optical specularity (P,), not to be confused with the coefficient of 
reflection, is indicated by: 
- 96 percent . p = - -  s A + B  
A 
If the presently indicated optical specularity (96 percent) of Echo I i s  compared 
with i ts  initial specularity a t  the t ime of deployment in orbit (12 August 1960), 
a n  actual r a t e  of specular degradation of aluminized Mylar due to the simul- 
taneously combined effects of all  environmental factors  in a near -ear th  orbit  
is inferred.  
cent. 
lar in a near-ear th  orbit  is indicated to be l e s s  than 1 percent per year: 
The initial optical specularity (Ps ) of Echo I was close to 98 pe r -  
0 
On this  basis  the actual ra te  of specular degradation for aluminized My- 
3 .55 years  1 .- antilog E 0 . 6  percent per year 
The photometric studies of Echo I a r e  being extended a t  Goodyear Aerospace 
Corporation under NASA-Langley Research  Center Contract NAS 1-31 14, moni- 
to red  by William J. O'Sullivan. While f i n a l  r e su l t s  f rom these additional visual 
and photoelectric measurements  a r e  not available a t  this t ime, the preliminary 
resu l t s  appear to support the conclusion herein that Echo 1 ' s  surface remains 
highly specular.  
-8- 
. 
Goodyear Aerospace GER-11521A 
SECTION I11 - SURFACE MACROTEXTURE ANALYSIS 
The photometric data were  a l so  used to determine mean and local radi i  of c u r -  
vature  of Echo 1's surface.  
surface having a coefficient of reflectivity of 0. 83 (typical for aluminized My- 
lar) can be found f rom the relation: 
The radius  of curvature  of a spherical  specular 
6 
Rc = antilog(1. 71806 - 0. 2m ) , SP 
where 
Rc = radius of curvature in feet, and 
m = stellar magnitude a t  a 1000-stat-mi zenith range for  
spherical  surface of 100 percent specularity, 83 percent 
reflectivity. 
sp 
To apply the above relation in the macrotexture  analysis,  it was f i r s t  necessary 
to eliminate the contribution of diffuse reflectivity, 2/3 BF($), f r o m  the nor-  
malized magnitudes. 
the representative specular normalized magnitude is: 
F r o m  the previous regress ion  analysis it can be seen that 
log q- A 
- = to. 264 , -0 .4  
which yields a mean R 
The normalized magnitudes a t  phase angles of 92. 2, 59. 3, and 35. 4 deg were 
selected for local rad i i  of curvature determinations because they corresponded 
to independent data extremes,  each a t  l eas t  2 <I f rom the best-fit and adopted 
regress ion  curve.  These magnitudes were  reduced in illuminance by the amount 
2/3 BF(+) to yield m = -0. 22, -0. 51, and to. 65, respectively, indicating in- 
SP 
dependent local curvatures  with radi i  of 58, 66, and 39 ft.  
of 46.3 ft .  
0 
- 9 -  
Goodyear Aerospace GER-11521A 
SECTION I V  - SIGNIFICANCE O F  RESULTS 
T h e  measurements  reported herein have provided the first available indica- 
tion of the actual degradation ra te  of a specular surface in a near -ear th  orbit  
and represent  a significant advance over the est imates  previously available 
for the design of solar energy collectors,  thermal  balance surfaces ,  e tc .  Re- 
peated observation and analysis would undoubtedly narrow the present range 
of uncertainty. 
pact tes t s  of very smal l  particles on aluminized Mylar,  these data should also 
prove useful in further defining the micrometeoroid environment at Echo 1 's  
orbi ta l  height, either with respect to the flux in the vicinity of the particle 
Together with the resu l t s  f rom laboratory hypervelocity im- 
m a s s  cutoff or  the m a s s  cutoff itself. 
These measurements  of Echo I can also serve  a s  a c r o s s  check on measure-  
ments  made by other methods of observation, such a s  by photoelectric or  
photographic photometry and high-resolution photography. 
the la t ter ,  Goodyear Aerospace with the cooperation of RCA Service Corpo- 
ra t ion personnel at  the Kennedy Space Center, made some "quick-try" a t -  
tempts  in 1962 to obtain high-resolution optical and electro-optical photo- 
graphs of Echo I, with uncertain resu l t s .  
one (or  more)  specular highlights were  being photographed repeatedly, and 
that Echo I was then sti l l  predominantly specular,  with some macrotexture  
variation. This conclusion is  entirely compatible with the recent  and m o r e  
definitive pho tometr ic indications. 
With reference to 
The tentative conclusion was that 
Because Echo I (and now a lso  Echo 11) is continually immersed  in the near -  
ear th  space environment and is continuing. to integrate the effects of a l l  the 
environmental parameters  a s  encountered throughout the course  of the ea r th ' s  
annual motion around the sun, it  is increasing in i ts  value both a s  a la rge-  
scale  tes t  specimen in a n  existing ideal tes t  for the technology of space ma- 
t e r i a l s  and as  a large-scale  scientific probe of the near -ear th  micrometeoroid 
-10- 
C 
1 Goodyear Aerospace GAP-11521A 
environment. 
sources  of vital information f o r  the astronaut ics  engineer and space scientist 
and deserve the ser ious investigations that traditional astronomy would de- 
mand and pursue for natural  satell i tes.  Artificial satell i tes tend to become 
"naturalized citizens" of space. 
It is suggested that Echo I and Echo I1 will continue to be 
-11-  
GER-11521A 
LIST OF REFERENCES 
1 .  MacRae, D. A. : "The Brightest Stars ,  It The Observer ' s  Handbook,l964. 
Toronto, The Royal Astronomical Societv of Canada. (Based on Johnson. 
H. L. ; and Morgan, W.  W .  : 
a r d s  of Spectral Type on the Revised System of the Yerkes Spectral Atlas, " 
Astrophysical Journal,  1953; 11 7: 113. ) 
"Fundamenial Stellar Photometry for Stand; 
2. Schneider, L. J .  : "Determination of the Stellar Magnitude Increment of 
the Echo I Satellite Due to the Ear th ' s  Albedo. I' SP-3225. Akron, Ohio, 
Goodyear Aerospace Corporation, 28 May 1964. 
3. Ginter, R. L. : "Albedo Radiation on a Sphere or Planet-Oriented Flat  
Plate.  It GER-11618. Akron, Ohio, Goodyear Aerospace Corporation. 
June 1964. 
4. Hardie, R. H. : "Photoelectric Reductions. " ChaDter 8 of Astronomical 
Techniques ( W .  A. Hiltner, e d . ) .  Chicago, I l l . ,  University of Chicago 
P r e s s ,  1962. 
5. Russell,  H. N. : Astrophysical Journal, 1916; 43:173. 
6 .  Baker,  R. M . ,  J r .  ; and Makemson, M. W .  : An Introduction to Astro-  
dynamics. New York, Academic P r e s s ,  1960, p. 252, 
7. GAP-1566: A Program for  the Purpose of Determining the Geometry, 
Surface Characterist ics,  and Reflectance Degradation Rate of the Echo I 
Satellite f rom Ground Observational Da ta .  Akron, Ohio, Goodyear Air - 
craf t  Corporation, 6 June 1962. 
-12- 


An indicated specular degradation rate for aluminized Mylar surfaces in near-earth orbit from recent photometric observations of the Echo I satellite

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